1. Field of the Invention
The present invention relates to recording devices such as an ink jet printer.
2. Discussion of the Background
A recording device employing an ink jet system records an image on a recording medium by discharging ink from a recording head while moving the recording head back and forth in the primary scanning direction to cause the ink to attach to the recording medium. Then, the recording medium is conveyed in the sub-scanning direction by transfer rollers, etc. to repeat recording in the main scanning direction and form the image on the recording medium.
However, the system of conveying a recording medium by transfer rollers involves a problem such that the assembly and eccentricity of the transfer rollers affect transfer (conveyance) of the recording medium. When the transfer amount of the recording medium varies, the image is formed at a position different from the target (ideal, theoretical) recording position on the recording medium.
Therefore, a technology that tried to deal with such a problem describes a method of adjusting the rotation of a transfer roller by recording a test pattern on a recording medium and detecting the shift amount of the recording medium along the transfer direction thereof based on the test pattern.
In this technology, a reference pattern (first pattern: e.g., refer to FIG. 20A) is recorded on a recording medium by nozzles situated on the upstream side in the recording head and an adjustment pattern (second pattern: e.g., refer to FIG. 20B) is recorded on a recording medium by nozzles situated on the downstream side in the recording head. Thus, a patch for adjustment at the first position (phase) of the transfer roller is formed.
Then, a reflection type optical sensor is used to measure the patch to obtain the dot deviation amount at the first position (phase). In addition, the dot deviation amount at the second position (phase) is also obtained by the same procedure. Next, the average deviation amount is calculated from the dot deviation amount at the first position (phase) and the dot deviation amount at the second position (phase). Thereafter, the correct instruction pulse value is calculated from the pulse adjustment value corresponding to the calculated average shift amount and the theoretical instruction pulse value.
The calculated correct instruction pulse value is set as the rotation amount of the transfer roller and the transfer roller is driven based on the pulse value.
However, in this technology, the patch for adjustment is formed while the recording head is moved in the main scanning direction. In addition, the reflection type optical sensor (detection device) is also moved in the main scanning direction in the same manner as in the recording head to calculate the dot deviation amount. Therefore, the average deviation amount calculated based on the dot deviation amount includes the difference ascribable to the movement of the recording head and the reflection type optical sensor. Therefore, no significant reduction in the variation in the sub-scanning direction according to the transfer roller is expected.